The decade after World War I saw the daring creation of the League of Nations: West European security had to be preserved through cooperation in transnational networks instead of through traditional multilateral expedients, and a new generation of diplomats had to enhance open diplomacy, push away the international, aristocratic elite, and democratize politics. Peace movements appeared on the international stage, and blew a fierce ideological wind over Europe. This hopeful change experienced its halcyon days around 1925-1928, when Europe as well as the Pacific encountered a true détente. This thesis deals with these changes in international security matters, incited by World War I and the subsequent creation of the League of Nations, and their consequences for Dutch foreign policy.